Effect of temperature and light on the stability of latanoprost and its clinical relevance

To examine the effect of controlled heat and ultraviolet exposures on the stability of latanoprost (Xalatan, Pharmacia & Upjohn, Kalamazoo, MI) using high-performance liquid chromatography to derive practical recommendations for patients regarding its use and storage.

Using serial dilution of a latanoprost stock solution, varying concentrations were prepared to obtain a standard curve. The accuracy and precision of the high-performance liquid chromatography assay conditions were validated using between-day and within-day studies. The original latanoprost containers were stored at 4, 25, 50, and 70 degrees C, and the concentration of latanoprost remaining was measured by high-performance liquid chromatography at different times for up to 1 month. In addition, the original latanoprost containers were exposed to known amounts of ultraviolet A and B radiation for 4 hours, and the concentration of latanoprost was measured at 1-hour intervals using high-performance liquid chromatography.

The increased temperature studies showed that latanoprost remained stable at 4 and 25 degrees C for the 30-day study duration. Analysis of concentration versus time curves for 50 and 70 degrees C yielded a t90 (time for 10% degradation) of 8.25 and 1.32 days, respectively. Ultraviolet B radiation caused a rapid degradation of latanoprost, whereas ultraviolet A radiation was less effective in causing the degradation of latanoprost.

Latanoprost exhibits thermal and solar instability and should ideally be stored below room temperature and in the dark. The importance of these storage conditions should be conveyed clearly to the patient.